Since April 19, 2000, 30 injecting-drug users (IDUs) died or were hospitalized with unexplained severe illness in Glasgow, Scotland. Illness was characterized by extensive local inflammation at a subcutaneous or intramuscular injection site often followed by hypotension and circulatory collapse. Since April 24, 2000, 15 IDUs in Dublin, Ireland, and 14 IDUs in England with similar illnesses have been identified. Despite debridement and broad spectrum antibiotics, 30 (51%) of the 59 patients in all three countries have died. This report further describes the clinical syndrome and key epidemiologic features of the illness as characterized by a preliminary investigation by health authorities in Scotland, Ireland, England, and the United States (1).